目录
- 目录
- 流程
- initApplicationEventMulticaster()
- registerListeners()
- finishRefresh()
- publishEvent()
- @EventListener处理
流程
容器的刷新流程如下：
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}其中与EventListener有关联的步骤
- initApplicationEventMulticaster(); 初始化事件多播器
- registerListeners(); 注册Listener到多播器
- finishBeanFactoryInitialization(beanFactory); 涉及将@EventListener转为普通Listener
- finishRefresh(); 发布容器刷新完成事件ContextRefreshedEvent
initApplicationEventMulticaster()
protected void initApplicationEventMulticaster() {
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
//找applicationEventMulticaster的组件
if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
this.applicationEventMulticaster =
beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
if (logger.isDebugEnabled()) {
logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
}
}
else {
//没有就创建一个
this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
//注册到beanFactory
beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
if (logger.isDebugEnabled()) {
logger.debug("Unable to locate ApplicationEventMulticaster with name '" +
APPLICATION_EVENT_MULTICASTER_BEAN_NAME +
"': using default [" + this.applicationEventMulticaster + "]");
}
}
}registerListeners()
protected void registerListeners() {
// Register statically specified listeners first.
for (ApplicationListener<?> listener : getApplicationListeners()) {
getApplicationEventMulticaster().addApplicationListener(listener);
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let post-processors apply to them!
String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
for (String listenerBeanName : listenerBeanNames) {
getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
}
// Publish early application events now that we finally have a multicaster...
Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
this.earlyApplicationEvents = null;
if (earlyEventsToProcess != null) {
for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
getApplicationEventMulticaster().multicastEvent(earlyEvent);
}
}
}finishRefresh()
protected void finishRefresh() {
// Clear context-level resource caches (such as ASM metadata from scanning).
clearResourceCaches();
// Initialize lifecycle processor for this context.
initLifecycleProcessor();
// Propagate refresh to lifecycle processor first.
getLifecycleProcessor().onRefresh();
// Publish the final event.
//发布事件
publishEvent(new ContextRefreshedEvent(this));
// Participate in LiveBeansView MBean, if active.
LiveBeansView.registerApplicationContext(this);
}publishEvent() 发布事件，我们也可以手动调用容器的publishEvent() 方法来发布事件
ApplicationContext.publishEvent(new MyEvent("test"));publishEvent()
protected void publishEvent(Object event, @Nullable ResolvableType eventType) {
// Decorate event as an ApplicationEvent if necessary
ApplicationEvent applicationEvent;
if (event instanceof ApplicationEvent) {
applicationEvent = (ApplicationEvent) event;
}
else {
applicationEvent = new PayloadApplicationEvent<>(this, event);
if (eventType == null) {
eventType = ((PayloadApplicationEvent) applicationEvent).getResolvableType();
}
}
// Multicast right now if possible - or lazily once the multicaster is initialized
if (this.earlyApplicationEvents != null) {
this.earlyApplicationEvents.add(applicationEvent);
}
else {
//获取多播器
getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);
}
// Publish event via parent context as well...
//父容器发布事件
if (this.parent != null) {
if (this.parent instanceof AbstractApplicationContext) {
((AbstractApplicationContext) this.parent).publishEvent(event, eventType);
}
else {
this.parent.publishEvent(event);
}
}
}@EventListener处理
原理：通过EventListenerMethodProcessor来处理@Eventlstener
public class EventListenerMethodProcessor implements SmartInitializingSingleton, ApplicationContextAware EventListenerMethodProcessor 是一个 SmartInitializingSingleton。
SmartInitializingSingleton什么时候执行呢？
在Refresh()
-> finishBeanFactoryInitialization(beanFactory);
-> DefaultListableBeanFactory#preInstantiateSingletons
public void preInstantiateSingletons() throws BeansException {
// Iterate over a copy to allow for init methods which in turn register new bean definitions.
// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) {
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
if (isFactoryBean(beanName)) {
Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
if (bean instanceof FactoryBean) {
final FactoryBean<?> factory = (FactoryBean<?>) bean;
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>)
((SmartFactoryBean<?>) factory)::isEagerInit,
getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
}
else {
// 创建bean
getBean(beanName);
}
}
}
// Trigger post-initialization callback for all applicable beans...
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton) {
final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
smartSingleton.afterSingletonsInstantiated();
return null;
}, getAccessControlContext());
}
else {
smartSingleton.afterSingletonsInstantiated();
}
}
}
}preInstantiateSingletons 前半部分主要是遍历beanNames 创建Bean。创建完bean后判断各bean是不是SmartInitializingSingleton，如果是则执行 smartSingleton.afterSingletonsInstantiated()方法。
//org.springframework.context.event.EventListenerMethodProcessor#afterSingletonsInstantiated
public void afterSingletonsInstantiated() {
List<EventListenerFactory> factories = getEventListenerFactories();
ConfigurableApplicationContext context = getApplicationContext();
String[] beanNames = context.getBeanNamesForType(Object.class);
for (String beanName : beanNames) {
if (!ScopedProxyUtils.isScopedTarget(beanName)) {
Class<?> type = null;
try {
type = AutoProxyUtils.determineTargetClass(context.getBeanFactory(), beanName);
}
if (type != null) {
if (ScopedObject.class.isAssignableFrom(type)) {
try {
Class<?> targetClass = AutoProxyUtils.determineTargetClass(
context.getBeanFactory(), ScopedProxyUtils.getTargetBeanName(beanName));
if (targetClass != null) {
type = targetClass;
}
}
}
try {
//处理bean
processBean(factories, beanName, type);
}
}
}
}
}protected void processBean(
final List<EventListenerFactory> factories, final String beanName, final Class<?> targetType) {
//没有注解的class
if (!this.nonAnnotatedClasses.contains(targetType)) {
Map<Method, EventListener> annotatedMethods = null;
try {
//查找被注解EventListener的方法
annotatedMethods = MethodIntrospector.selectMethods(targetType,
(MethodIntrospector.MetadataLookup<EventListener>) method ->
AnnotatedElementUtils.findMergedAnnotation(method, EventListener.class));
}
catch (Throwable ex) {
// An unresolvable type in a method signature, probably from a lazy bean - let's ignore it.
if (logger.isDebugEnabled()) {
logger.debug("Could not resolve methods for bean with name '" + beanName + "'", ex);
}
}
if (CollectionUtils.isEmpty(annotatedMethods)) {
//添加到没有注解的集合
this.nonAnnotatedClasses.add(targetType);
if (logger.isTraceEnabled()) {
logger.trace("No @EventListener annotations found on bean class: " + targetType.getName());
}
}
else {
// Non-empty set of methods
ConfigurableApplicationContext context = getApplicationContext();
for (Method method : annotatedMethods.keySet()) {
for (EventListenerFactory factory : factories) {
if (factory.supportsMethod(method)) {
Method methodToUse = AopUtils.selectInvocableMethod(method, context.getType(beanName));
//创建applicationListener，通过Adapter将注解形式的listener转换为普通的listener
ApplicationListener<?> applicationListener =
factory.createApplicationListener(beanName, targetType, methodToUse);
if (applicationListener instanceof ApplicationListenerMethodAdapter) {
((ApplicationListenerMethodAdapter) applicationListener).init(context, this.evaluator);
}
//添加listner到applicationContext
context.addApplicationListener(applicationListener);
break;
}
}
}
if (logger.isDebugEnabled()) {
logger.debug(annotatedMethods.size() + " @EventListener methods processed on bean '" +
beanName + "': " + annotatedMethods);
}
}
}
}- 查找类中标注@EventListener的方法
- EventListenerFactory.createApplicationListener(beanName, targetType, methodToUse) 构造listener
添加listener到Context中
- 如果有applicationEventMulticaster，添加到ApplicationContext.applicationEventMulticaster中
- 如果没有applicationEventMulticaster，添加到ApplicationContext.applicationListeners中。
